No promo code is needed for Google Play, but for Amazon you’ll need to enter MOVIE75OFF as follows:
Need to apply your promotional code? Click “More Purchase Options”, followed by “Redeem a gift card or promotion code”. Once the code has been entered, exit the pop-up window and click the “Rent Movie HD” or “Rent Movie SD” option. While onsite pricing will not reflect your discount, your order history and purchase confirmation email will show the total discount applied to your order.